The present invention relates to the production of co-extruded multiple-layered sheeting or film from chemically and/or physically different polymeric materials which have hitherto been found extremely difficult to unite by conventional extrusion techniques. More particularly, the present invention relates to the production of a composite co-extruded sheeting or film of normally difficultly bondable solid hydrocarbon polymers and ABS polymers which possess excellent peel strengths between each layer.
Many attempts have been made to produce a thermoplastic sheeting or film which combines the desirable characteristics of several polymeric materials. Due to the highly attractive economic characteristics of solid hydrocarbon polymers and the highly desirable surface properties of ABS polymers, the prior art has particularly sought to produce a sheeting or film which combines the desirable properties of each of these polymers. Heretofore, however, the prior art has been unable to achieve a sheeting or film of solid hydrocarbon polymers and ABS polymers which possess a satisfactory quality and peel strength. One method by which the prior art has sought to prepare a sheeting or film from these two types of polymeric materials has involved the blending of the ABS polymer and the solid hydrocarbon polymer. This technique has not been entirely successful, however, since the properties of each material are usually altered to an undesirable degree as a result of the blending. Additionally, the physical and chemical incompatibility of the ABS and solid hydrocarbon polymers has prevented the preparation of a satisfactory product.
In another technique, preformed layers of each polymer are adhered together by interposing an adhesive between each preformed layer of polymer. Here again, however, the relative incompatibility of the solid hydrocarbon polymers and the ABS polymers has resulted in a composite sheeting or film with less than desirable physical properties. Moreover, this technique requires a plurality of steps involving molding each polymer layer, applying a suitable adhesive thereto, superimposing the adhesive coated polymer layers upon one another, and then pressing the sheets into a unitary, composite material. Additionally, in order to produce acceptably thin composites in this manner, very thin polymer layers must be utilized which are extremely difficult to work with. For example, in Japanese Kokai 74-39,656, separate sheets of high impact polystyrene and ABS polymers are first extrusion molded. A butadiene-styrene block copolymer is then utilized as an adhesive to prepare a laminate from the preformed extrusion molded sheets. In a variation of this technique, U.S. Pat. No. 3,809,602 describes the preparation of a composite sheeting of ABS polymer and polyvinylidene chloride. In the method of this patent, a preformed sheet of ABS polymer is coated with a layer of adhesive. After drying, an emulsion of the polyvinylidene chloride polymer is then applied to the adhesive side of the ABS sheet. Another drying step is thereafter required to complete the composite sheet.
Polymer composites of ABS and solid hydrocarbon polymers have also been sought to be prepared by co-extrusion. Very little success, however, has been recorded in the area of co-extrusion of multiple thermoplastic layers merely laminated on top of one another. It is well known in the art that solid hydrocarbon polymers and ABS polymers exhibit a poor adhesion with each other. Polystyrene polymers and ABS polymers of 20% or more acrylonitrile content are particularly known to exhibit poor adhesion to each other. Prior attempts aimed at coextrusion of these polymeric materials have resulted in multiple-layered products wherein the individual layers are rather easily peeled from one another, and like attempts to laminate materials of this nature by extruding a molten layer of one polymer onto a preformed sheet of a second polymer have provided similar unsatisfactory results. One exception to the general inability of the prior art to manufacture composite products of solid hydrocarbon and ABS polymers is described in U.S. Patent Application Ser. No. 752,619, now U.S. Pat. No. 4,100,237. This application describes a particularly efficacious method for the co-extrusion of a multiple-layered sheeting of ABS polymer and polystyrene. However, the method of this application is limited to a two-layer structure in which the ABS polymer has a specific range of permissible acrylonitrile content.
Accordingly, there exists a great need in the art for a multiple-layered sheeting or film which combines the desirable properties of a wide variety of ABS and solid hydrocarbon polymers, and which at the same time exhibits a satisfactory peel strength between each layer.